The invention relates to a deflecting element comprising a first substrate and a second substrate enclosing a liquid crystalline material which is switchable, a surface of one of the substrates facing the liquid crystalline material being provided with a grating structure.
The invention also relates to an optical deflector provided with such a deflecting element.
A deflecting element of the type described in the opening paragraph is known from British patent specification GB 2 184 560. The element described in this document comprises a liquid crystalline layer which is enclosed between two electrodes. The surface of one of the electrodes is provided with a grating at the side of the liquid crystalline material. Two effects play a role here. When a light beam passes through a grating, the light beam will be spread into all directions due to diffraction on the grating lines. For a monochromatic, coherent light beam such as, for example a beam of given laser types, destructive interference will occur in given directions and constructive interference will occur in other directions. The angles at which constructive interference occurs are determined by the wavelength of the light and the refractive index of the medium in which diffraction takes place. By changing the refractive index of the medium from which the beam originates and/or of the medium in which the beam arrives, the angle at which the beam leaves the grating can be varied. In accordance with said British patent specification, a switchable liquid crystalline material is therefore provided on the grating. By applying an electric voltage across the liquid crystalline material, the refractive index of the material is changed and the angle at which constructive interference occurs can be adjusted.
A drawback of the deflecting element described above is that, for the beam exiting from the element, a light deflection caused by the difference in refractive index between the two media will occur at the interface between the liquid crystalline material and the second substrate. In this way, the exit angle is only a function of the angle of incidence and is not a function of the refractive index of the liquid crystalline material.